Various example embodiments of the present inventive concepts relate to a peripheral component interconnect express (PCIe) device, and more particularly, to a PCIe device for supporting a separate reference clock with independent spread spectrum clocking (SSC) (SRIS), which can automatically select one reference clock signal output from several different clock sources as an operating clock signal.
In general, a reference clock signal with a frequency of 100 MHz is used in a PCIe system including a PCIe host and a PCIe device. A method of supplying the reference clock signal can be classified into a common referenced clock signal method and an individual reference clock signal method.
The common reference clock signal method is a method in which a PCIe device and a PCIe host share one reference clock source, the reference clock source being embodied in the PCIe host. In the common reference clock signal method, a reference clock signal is generated by the reference clock source and is supplied to the PCIe device through a PCIe connector. A pin for supplying the reference clock signal is required to be assigned in the PCIe connector.
The individual reference clock signal method is a method in which a PCIe device and a PCIe host each have different reference clock sources, respectively, and the reference clock sources of the PCIe device and the PCIe host each generates a respective reference clock signal to be used in operation by the corresponding PCIe device or the PCIe host. In this case, the PCIe device and the PCIe host may be connected to each other using a PCIe cable, or the like, and the PCIe cable does not require a pin for supplying a reference clock signal.